Limit control



A. L. JUDSON Dec. 4, 1956 LIMIT CONTROL Filed May 3. 1954 INVENToR. /ef/ Jua/5077 HEL/V 7- United States Patent LIlVII'I CONTROL Albert L. Judson, Portland, Oreg., assignor to Iron Fireman Manufacturing Company, Portland, Oreg.

Application May 3, 1954, Serial No. 427,125 3 Claims. (Cl. 20D-S3) This invention relates generally to limit control instruments adapted to be preset at desired lower and upper limits of a variable condition and to indicate the attainment of the preset limits. More particularly this invention relates to limit control instruments of the above noted type in which the attainment of one preset limit is indicated by the closing of an electric switch to energize a means adapted to reverse the trend of variation of the condition.

Specifically to show a valuable use for this invention and a structure through which the invention is usefully practiced the explanation herein contained will be directed to an electric limit switch responsive to a variable pressure to which the instrument could be calibrated if desired. However, to more completely show the usefulness of the system the instrument is calibrated and described as a temperature responsive instrument and provided with a transducing means for changing a temperature variation to an equivalent pressure variation.

ln the automatic control of home heating equipment to which the form of control here described is adapted a direct acting limit control is required to limit the temperature of the medium circulated to heat the home while a reverse acting limit control is required to hold otf the circulation of the heating medium until it is warm enough to be effective for its purpose. In many cases a direct acting instrument and a reverse acting instrument are both assembled in the same case to further the appearance of this installation and the convenience of making the installation.

The modern trend in limit control design is to start with a totally enclosed electric switch of the so-called unit type and design a mechanism to combine with it to actuate it. The unit switches are provided in both direct and reverse acting types so that the same mechanisms can be used for both types of controls. However, somewhere in the mechanism of the control an adjustment is required for adjusting at the factory, the mechanism to balance with the switch biasing spring and contact setting of the switch. This is not a matter which can properly be done in the Alield or by the installer and therefore it is not practical to change the instrument in the field from one type of action to the other by changing unit switches. Previously it has been necessary for the factory to make and the dealer to stock both direct and reverse action types of instruments.

lt is a particular object of this invention to provide a limit control instrument of the kind described which can easily be changed from direct to reverse acting, or vice versa, in the field without changing its calibration or changing parts or requiring special tools.

lt is a second object of this invention to provide such an instrument with a convenient and novel means for adapting the mechanism at the factory to the characterstics of the particular unit switch with which it is assembled.

It is a third object to provide such an instrument which is rugged and simple in construction, low in first 2,773,147 Patented Dec. 4, 1956 ILCC cost and cost of maintenance, convenient to set, and small 1n srze.

How these and other objects are attained is explained in the following description referring to the attached drawing in which- Fig. 1 is a plan view with the setting knob removed of one form of instrument in which this invention is practiced.

Fig. 2 is a longitudinal vertical sectional view through the mechanism of Fig. 1.

Fig. 3 is a fragmental longitudinal sectional view similar to Fig. 2 but with the switch actuating parts reversed in action.

Fig. 4 is a plan view o f the dial and setting knob of the instrument shown in Fig. 1.

Like numerals of reference indicate like parts in the several figures of the drawing.

Referring now to the drawing the instrument base 11 is shown to be a substantially rectangular box open at the bottom, closed at the ends, having a substantially liat top 12, having substantially flat sides 13, 14, the lower ends of the sides being out-turned to form substantially flat anges 15, 16, respectively in the same plane.

Secured to the top 12 of the base 11 by screws (not shown) is the insulating case 17 of the unit type electric switch of the instrument. The internal working and parts of the unit switch are not shown since similar switches are available from many manufacturers and are well known in the art. Formed on the lower side of switch case 17 is switch operating stem guide 18 extending through hole 19 formed through flat top 12 of base 11. Switch operating stem 20 extends slidably through guide 1S into the interior of base 11. The unit switch is of normally closed design and is opened on a required length of upward movement of stem 20. Terminal wires (not shown) for the circuit to be controlled are connected by screws 21 to the switch terminals set in the top of case 17.

Secured to base flanges 15, 16 by screws 22 threaded into holes 23 is a temperature sensitive unit 24 of the liquid till type well know in the art. The temperature sensitive element includes a rigid iianged cup 25 to which is hermetically sealed through a communicating fitting 31 the small diameter metal tube 26 of such selected length as will extend from the mounting position of the instrument to a location where the condition change is to be sensed. At the location of the condition change the small tube is hermetically sealed in a bulb or a concentration of larger tubing 27 as shown. A cup shaped exible metal diaphragm 28 is hermetically sealed at its open end ange 29 to the flange of cup 25 thus making a sealed enclosure of the space 30 between the heads of cups 24, 28 and including the interiors of tubes 26, 27. This space is completely filled with a liquid having a required coetiicient of thermal expansion for the range over which the instrument is to operate. Heating of the liquid as shown by the arrows 32 causes the head 33 of cup 28 to move upward carrying with it push rod 34 against the bias of fulcrum spring 35 conned longitudinally between the top 12 of base 11 and collar 36 of push rod 34. The upper end of push rod 34 is seen to be piloted in a hole 37 formed in top 12.

As shown in Fig. 2 two generally channel shaped levers 38, 39 formed with registering keyhole slots 40,

- 41 in their respective back elements 42, 43 are sized to nest with lever 3S within lever 39. Each of the levers 38, 39 are formed at their left ends with two vertical side extending ears 44 perforated by bearing holes 45 for pivot pin 46 adapted pivotally to connect, as shown, levers 38 and 39 and both to channel shaped switch lever 47 wider than lever 39. Before the assembly of temperature sensitive unit 24 to base 11, levers 38, 39

l i? pivoted to lever 47 are moved up over push rod 34 with rod 34 passing through the larger end of keyhole slots 4t), di after which the levers are moved to the left tor the necked portion of push rod fibelow the shoulder 36 to occupy the narrow end of keyhole slots 40, di iu levers 3S, 39. With the levers in this position, as shown in Fig. 2, switch lever 47 is pivoted to sides 13, ld of base 11 by pivot pin 43 through holes 49 in the legs of lever 47 and holes 5t) in side l, M. (See Fig. 3.) Laterally of the small ends of key slots et), :1, levers 38 and 39 are formed with upward and downward ridges respectively as shown to form definite lines oi, bearing of levers 33, 39 on push rod 34.

The right end end of lever 39 is formed with a locator 51 for spring 52. The legs of lever 38 are cut away at the right and its back is offset as at 53, the odset end 53 having a threaded hole therethrough to receive screw 54 the head of which is accessi-ble through a. hole 55 formed in top l2 of base lll. The upper end of spring 52 is tted with a shouldered plug 56 formed with a central depression (not shown) adapted to receive the lower end of screw 54 and to be guided thereby. Threading screw 5ft downwardly through offset 53 moves plug 56 downward and with it the upper end of spring 52 thus increasing the separating force of spring 52 on the free ends of levers 38, 39.

Formed upwardly on top l2 of base lll'l is a circular ilat topped dome 57 formed with a central hole therethrough adapted to receive the reduced diameter lower end of stem adjusting nut 53 which is then spun over on the underside of dome 57 to secure nut 58 thereto. Main stem 59 having an axial bore therethrough and an internally threaded larger bore at its top end is externally threaded, as shown in Fig. 2, to be threaded into nut 5S. Main stem 59 is twice reduced in outer diameter at its top end, the larger of the two reduced diameter sections being adapted rotatably to journal stop arm 60. The smaller reduced diameter end section of main stem 59 tits neatly through a central hole in dial knob plate 61. and is riveted thereover to secure knob plate di. to main stem 59 and rotatably secure stop arm 60 to main stem 59.

Dial knob plate 61 is perforated with an arcuate slot 62 adapted to register with a threaded hole, not shown, formed in stop arm 6h. Screw 63 formed with a head larger than the width of slot 62 is entered through slot o2 and threaded into the hole in stop arm 60 and tightened to secure stop arm o@ to knob plate 6.11. Radially extending stop 64 on knob plate 61 and radially extending stop 65 on stop arm 6h limit the rotation of main stem 59 in either direction by Contact with stationary stop 65 secured to dial support 67 secured to base lli.

Dial 6d formed with a central hole 69 and dial markings 7tl thereabout is supported on dial support 67. See Figs. l and 4. Dial knob 7i formed with indicating arrow 72 on its top and an arcuate gap 73 at its outer diameter is secured to plate 6i by screws 74 threaded into holes 75 in plate 61.

Externally threaded to spirally engage the internal threads at the upper end of main stem 59 is diierential adjustment nut 76 with diiferential pointer 77 fixed thereto. Differential nut friction spring 84 confined within main stem 59 by nut 76 adds friction loading to the rotation of nut 76 in stem 59. Extending upwardly from pointer 77 through gap 73 in knob 71 is extension 7S adapted to be manually engaged to be positioned within the limits of gap 73 to position pointer 77 and thereby determine the vertical position relative to stern 59 of differential adjustment nut 76.

Main stern friction spring 82 is axially confined between the under side of dome 56 in top i2 of base il and spring cup 81 axially retained on main stem S9 by C-washer 83.

Differential rod 79 with head Si) at its lower end and externally threadedv at its upper end passes loosely through d registered holes in back elements 42, 43 of levers 38, 39, respectively and slidably axially through main stem S9 and threaded into differential nut 76 to which it is locked by set screw 35 threaded downwardly into nut '76.

As described with reference to Figs. l, 2, and 4 the instrument of this invention operates as a direct acting or upper temperature limit switch. As the bulb or tube concentration 27 gets warmer the filling liquid expands and the increase in pressure in space 3'9 pressures diaphragm 33 and push rod 3d upwards against the bias of fulcrum spring 35. Push rod 34 as it moves upwards presses against back 43 of lever 39 which fulcrumed about spring S2 at its right end moves its left end upward. On its upward movement the left end of lever 39 rotates lever 47 counterclockwise about pivot pin d8 until the right end of lever 47 strikes the operating stem 2t) of the unit switch. Switch operating stein 2t) is spring biased towards its downward po-sition. With lever 47 against stern 2t) on further upward movement of rod 34, Spring 52 gradually shortens until dimple So formed upwardly in back 43 of lever 39 contacts the underside of back 42 of lever 3S. On further upward movement of rod 34 levers 33, 39 move as one. Fulcrumed about the lower end of main stem 59, the upward movement of the left ends of levers 38, 39 press the right end of lever 157 farther upward taking switch stem 20 along with it until at the position indicated by the dash dot line S7 the switch is operated to open position.

It is understood that the instrument is so constructed and calibrated that the switch opens at the temperature of bulb 27 indicated on dial marking 70 by the arrow 72 on knob 7l. When the switch is opened the means (not shown) for heating bulb 27 is deenergized and bulb 27 thereafter starts to cool reducing the pressure in space 36B and allowing rod 34 gradually to recede vdownwardly as biased by spring 35.

As bar 34 moves downwardly away from lever 39, the right end of lever 39 moves downwardly until its back 43 strikes head Si@ of dilerential rod 79 and collar 36 of push rod 34 strikes back i2 of lever 38 after which the bias or" spring 35 added to that of the switch stem biasing spring rotates levers 38, 39 in a counterclockwise direction about head 80 of rod 79 and at a desired differential temperature of bulb 27 below the switch opening temperature the switch will close. It is understood that the instrument is so constructed and calibrated that the temperature differential at which the switch is closed will be that indicated on dial marking 7? by differential pointer 77.

As making possible the above operation it is seen that spring 52 and its adjustment by screw 54 are adapted to balance in action with the biasing spring of switch stem 2t) and that the desired temperature differential of the switch is controlled by the distance between head Si? of rod 79 and the lower end of main stem S9 as determined by the rotation of differential nut 76 with respect to stem 59 with which it is threadedly engaged.

That with a simple interchange of a single part the direct acting instrument of Figs. l, 2, and 4 is changed to a reverse acting instrument without change of parts or recalibration is shown in Fig. 3 in which pin 43 is removed from holes 50 in base 1E and holes 49 in lever i7 and placed in holes 8 in base l1 and holes S9 in lever 47 to pivot lever 47 for clockwise rotation about pin 43 when the temperature of bulb 27 increases. It is seen that when bulb 27 is cold lever 47 will stand with its right end rotated upwardly to hold switch stern 2? in its upward or switch open position shown in Fig. 3 and by dash dot line 87 in Fig. 2. As thus arranged thc switch operates as a low temperature limit switch to prevent the operation of an air conditioning air circulating fan if the air to be circulated is too cold for comfort. When the temperature of bulb 27 rises to a comfort temperature push rod Se will have risen as previously described until lever 47 will have rotated to the position shown by dash dot line 90 and the switch will close to actuate the fan.

Having thus stated some of the objects of this invention, described and illustrated a preferred way in which the invention may be operatively formed, I claim:

1. An alternative direct or reverse acting limit control comprising a frame, an electric switch secured on said frame, said switch having an open position and a closed position, a condition responsive means secured on said frame, an actuating lever for said switch, a pivot pin, said frame and said lever having a rst set of bearings for said pivot pin formed thereon and a second set of bearings for said pivot pin formed thereon, said actuating lever being adapted when pivoted to said frame by said pm 1n either of said sets of bearings to rotate in the same direction about said pin to operate said switch to one of its said positions, a second lever, a third lever, means hinging one end of each of said second and third levers to said actuating lever at a point intermediate said first and said second bearing positions, the free ends of said second and third evers extending in the same direction from said hinging means, means resiliently biasing the free end of said second lever from the free end of said third lever, adjustable stop means carried on said frame, means adapting said adjustable stop means to limit the movement of said second and said third levers by said resilient biasing means, and means adapting said condition responsive means to rock said second and third lever about said adjustable stop means to rock said actuating lever at said hinging means about said pivot pin to actuate said switch between its open position and its closed position, said control being direct acting when said pivot pin is engaged in one of said sets of bearings and reverse acting when said pivot pin is engaged in the other of said sets of bearings.

2. in a control structure, a frame, a rst lever pivotally mounted on said frame, a second lever, a third lever, one end of each of said second and third levers being hingedly secured to said rst lever, means biasing the free end of said second lever from the free end of said third lever,

a rst adjustable stop means carried on said frame adapted to limit the rotation of said second lever in the direction of its bias, a second adjustable stop means carried on said frame adapted to limit the rotation of third lever in the direction of its bias, a condition responsive means secured to said frame, an electric switch carried on said frame, said switch having two positions of operation, means adapting said condition responsive means lto rock said second and third levers about said adjustable stop means to rock said first lever about its pivot position on said frame and means adapting said rst lever when actuated by said condition responsive means through said second and third levers to operate said switch between its two positions of operation.

3. A dual purpose limit switch for a .condition changing means, said limit switch comprising a frame, an electric switch secured to said frame, a condition responsive means secured to said frame, an actuating lever for said electric switch, a pivot pin, said actuating lever and said frame being formed with a iirst set of bearings for said pivot pin and a second set of bearings for said pivot pin, additional lever means interposed between said condition responsive means and said actuating lever, and hinge means connecting said additional lever means to said actuating lever at a hinge point on said actuating lever intermediate said rst set of bearings and said second set of bearings formed on said actuating lever, whereby when said pivot pin engages said frame and said actuating lever at one of said sets of bearings said limit switch will be direct acting and when said pivot pin engages said frame and said actuating lever at the other of said sets of bearings said limit switch will be reverse acting.

References Cited in the le of this patent UNITED STATES PATENTS 2,353,075 Hennecamp July 4, 1944 2,389,436 Kearney Nov. 20, 1945 2,436,906 Svoboda Mar. 2, 1948 2,480,538 Barr Aug. 30, 1949 2,492,675 Yeida Dec. 27, 1949 

